Method for manufacturing a metal sheet with a ZnAl coating and with optimized wiping, corresponding metal sheet, part and vehicle

ABSTRACT

A steel part includes a steel sheet substrate and a coating on at least one surface of the steel sheet substrate. The coating includes between 0.2 and 0.7% by weight of Al, with a remainder of the metal coating being Zn and inevitable impurities. The steel sheet substrate and the coating have at least one deformation. An outer surface of the coating has a waviness Wa0.8 of less than or equal to 0.43 μm.

This application is a continuation of U.S. Ser. No. 15/826,037, filed onNov. 29, 2017, which is a continuation of U.S. Ser. No. 14/442,955,filed on May 14, 2015, which is National Stage Entry of InternationalApplication No. PCT/IB 2014/058879, filed on Feb. 10, 2014, which claimspriority to International Application No. PCT/FR2013/050479, filed Mar.6, 2013, the disclosures of which are hereby incorporated by referenceherein.

The present disclosure relates to a method for making a metal sheetcomprising a steel substrate, at least one face of which is coated witha metal coating comprising Al, the remainder of the metal coating beingZn, inevitable impurities and optionally one or several additionalelements selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr, orBi, the weight content of each additional element in the metal coatingbeing less than 0.3%, the metal coating having an aluminium weightcontent comprised between 0.2 and 0.7%, the method comprising at leaststeps for:

-   -   providing the substrate,    -   depositing a metal coating on at least one face by dipping the        substrate in a bath in order to obtain the metal sheet,    -   wiping the metal coating with at least one nozzle projecting        through at least one outlet a gas for wiping the metal coating,        the metal sheet running in front of the nozzle and the gas being        ejected from the nozzle along a main ejection direction, and    -   solidifying the metal coating.

Such a metal sheet is more particularly intended for making body partsfor a land motor driven vehicle such as an automobile.

The metal sheet is then cut out and deformed in order to form the bodyparts or the body.

This body is then coated with a film of paint (or paint system) whichensures a good aspect of the surface and participates with the metalcoating based on zinc, in protection against corrosion.

BACKGROUND

Coatings based on zinc of metal sheets have what is called a waviness oftheir outer surfaces, which can presently only be compensated bysignificant thicknesses of paint, under the penalty of having aso-called “orange peel” aspect, unacceptable for body parts.

The waviness W of the outer surface of a coating is a smoothpseudo-periodic geometrical irregularity with quite long wavelength (0.8to 10 mm) which is distinguished from roughness R which corresponds togeometrical irregularities with short wavelengths.

SUMMARY

In the present disclosure, the arithmetic mean Wa of the wavinessprofile, expressed in μm, was retained for characterizing the wavinessof the outer surface of a metal sheet coating, and the waviness ismeasured with 0.8 mm a cut-off threshold and designated by Wa_(0.8).

A reduction in the waviness Wa_(0.8) may allow reduction of thethickness of the paint film used for attaining a given property of paintaspect or, for constant thickness of the paint film, an improvement inthe quality of the paint aspect.

A method is provided for making a metal sheet, comprising a substrate,for which at least one face was coated by dip coating with a metalcoating based on zinc and comprising between 0.2 and 0.7% by weight ofAl, the outer surface of the metal coating having reduced wavinessWa_(0.8).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be illustrated by examples given as an indication,and not as a limitation, and with reference to the appended figureswherein:

FIG. 1 is a schematic sectional view illustrating the structure of ametal sheet according to an embodiment of the invention,

FIG. 2 is a schematic side view illustrating a tank and wiping nozzlesfor making the metal sheet of FIG. 1 ,

FIG. 3 is a partial, schematic and enlarged view of the circled portionIII of FIG. 2 , and

FIG. 4 is a schematic view taken along the arrow IV of FIG. 3 , andillustrating the shape of the output of the nozzle of FIG. 3 .

DETAILED DESCRIPTION

The metal sheet 1 of FIG. 1 comprises a steel substrate 3 coated on eachof its two faces 5 with a metal coating 7.

It will be observed that the relative thicknesses of the substrate 3 andof the different layers coating it have not been observed in FIG. 1 inorder to facilitate the illustration.

The coatings 7 present on both faces 5 are similar and only one will bedescribed in detail subsequently. Alternatively (not shown), only one ofthe faces 5 has a coating 7.

The coating 7 generally has a thickness of less than or equal to 25 μmand aims at protecting the substrate 3 against corrosion.

The coating 7 comprises zinc and aluminium. The aluminium weight contentof the metal coating 7 is comprised between 0.2 and 0.7%, preferablybetween 0.2 and 0.6%, and still more preferably between 0.2 and 0.5%. Asindicated below, the limits of these aluminium content ranges aregreater than those of the bath used for making the coating 7. This isexplained by the formation of intermetallic substances at the junctionbetween the substrate 3 and the coating 7 which leads to an increase inthe aluminium content in the coating 7.

For making the metal sheet 1, it is possible for example to proceed asfollows.

A substrate 3 as a strip obtained for example by hot and thencold-rolling is used.

Preferably, for cold-rolling, one starts by cold-rolling the substrate 3with a reduction rate generally comprised between 60 and 85%, so as toobtain a substrate 3 with a thickness for example comprised between 0.2and 2 mm.

In a preferred embodiment, one makes sure that at least the lastcold-rolling pass is carried out with so-called «smooth» work rolls,i.e. rectified and non-etched rolls, for which the work surfaces have aroughness Ra_(2.5), i.e. measured with a cut-off threshold at 2.5 mm,less than 0.5 μm.

It is recalled that work rolls are the rolls of the rolling milldirectly in contact with the substrate 3 for ensuring its deformation.One refers, with the term of work surface, to their surfaces in contactwith the substrate 3.

The smooth work rolls will be present at least in the last cage(s) ofthe rolling mill when the running direction of the substrate 3 in therolling mill is considered.

The use of smooth work rolls at least for the last pass gives thepossibility of better controlling the waviness Wa_(0.8) of the metalsheet 1 obtained subsequently by coating of the substrate 3 on the onehand and parts which may be produced by deforming the metal sheet 1 onthe other hand.

In particular, such cold-rolling allows reduction in the wavinessWa_(0.8) as compared with rolling only resorting to rolls with strongerroughness, etched either by shot-blasting, or by an electric discharge(so-called Electron Discharge Texture (EDT) rolls), or further by anelectron beam (so-called Electron Beam Texture (EBT) rolls).

The cold-rolled substrate 3 may then be subject to annealing conductedin a conventional way in an annealing oven under a reducing atmosphere,with view to recrystallization after the work hardening which it hasundergone during the cold-rolling operation.

Recrystallization annealing further gives the possibility of activatingthe faces 5 of the substrate 3 so as to promote the chemical reactionsrequired for the subsequent dip-coating operation.

Depending on the grade of the steel, the recrystallization annealing iscarried out at a temperature comprised between 650 and 900° C. for aperiod required for recrystallization of the steel and for activation ofthe faces 5.

The substrate 3 is then cooled to a temperature close to that of a bath13 contained in a tank 15.

The composition of the bath 13 is based on zinc and contains between 0.1and 0.5% by weight of aluminium, preferably between 0.1 and 0.4%, andstill preferably between 0.1 and 0.3%.

The composition of the bath 13 may also contain up to 0.3% by weight ofoptional addition elements such as Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce,Cr, Ni, Zr or Bi.

These different elements may inter alia allow improvement in theresistance to corrosion of the coating or else its brittleness or itsadhesion, for example.

One skilled in the art who is aware of their effects on thecharacteristics of the coating will know how to use them according tothe sought additional purpose. It was also checked that these elementsdid not interfere with controlling the waviness obtained by the methodaccording to the present disclosure.

Finally, the bath 13 may contain inevitable impurities from ingots forfeeding the tank or else further from the passage of the substrate 3 inthe bath 13. Mention may thus be notably made of iron.

After passing in the bath 13, the substrate 3 is coated on its two faces5 with the coating 7 for obtaining the metal sheet 1.

As illustrated by FIG. 2 , the metal sheet 1 is then subject to wipingby means of nozzles 17 placed on either side of the metal sheet 1 andwhich project a wiping gas, for example air or an inert gas, towards theouter surfaces 21 of the coating 7. The wiping gas is ejected from eachnozzle 17 along a main ejection direction E. The main ejectiondirections E of each nozzle 17 are materialized in dotted lines in FIGS.2 and 3 .

In the illustrated example, the directions E are horizontal andorthogonal to the metal sheet 1. In other embodiments, the directions Emay have other inclinations relatively to the metal sheet 1.

The running speed V of the substrate 3 on the production line used andtherefore in front of the nozzle 17 is generally comprised between 80m/min and 300 m/min, and it is preferably greater than 120 m/min, oreven 150 m/min.

In order to limit oxidation of the coating 7, provision may be made fora confinement box 23 for confining the atmosphere around the metal sheet1 downstream from the nozzle 17. The term of downstream is meant hererelatively to the running direction S of the metal sheet 1 facing thenozzles 17.

The confinement box 23 may alternatively be extended upstream as far asthe surface of the bath 13 or as far as an intermediate position betweenthe nozzle 17 and the surface of the bath 13.

In certain alternatives, the installation may not comprise anyconfinement box.

In the example described above, the nozzle 17 has structures, positionsrelatively to the metal sheet 1 which are similar and they operate withsimilar adjustments. Thus, only the right nozzle 17 of FIG. 2 will bedescribed below, with reference to FIG. 3 .

Alternatively, the nozzle 17 may have different structures, differentpositions and/or operate with different adjustments. It is also possibleto only provide a nozzle on one side of the metal sheet 1.

The nozzle 17 has an outlet 25 through which the wiping gas is ejectedtowards the outer surface 21 of the coating 7 placed opposite. Variousouter shapes may be contemplated for the nozzle 17.

The outlet 25 of the nozzle 17 is positioned at a distance Z from themetal sheet 1 along the main ejection direction E. As illustrated byFIG. 4 , the outlet 25 generally appears as a slot which extends,perpendicularly to the running direction S and to the plane of FIG. 3 ,over a width L at least equal to the width of the metal sheet 1.

Generally, the height of the outlet 25, i.e. its dimension parallel tothe running direction S of the metal sheet 1 in front of the nozzle 17,is constant as illustrated by FIG. 4 . This being the case, in certainalternatives, this height may vary over the width of the outlet 25.Thus, the outlet 25 may have for example a slightly flared shape towardsits end (shape of a bowtie).

In order to take into account these possible height variations and thedifferent possible embodiments, the average height d of the outlet 25 onits width L will be considered subsequently.

The pressure of the wiping gas in the nozzle 17 is noted as P and thevolume fraction of oxygen in the wiping gas is noted as fO₂.

According to the present disclosure, at least one of the followingequations is observed:

$\begin{matrix}{{\frac{Z}{d} + {18{\ln\left( \frac{Z}{d} \right)}}} < {{8{\ln\left( \frac{P}{V} \right)}} - 27.52}} & (A) \\{{fO}_{2} < \frac{2.304{.10}^{- 3}}{\left( {27.52 + \frac{Z}{d} + {8{\ln\left( {\frac{V}{P}\left( \frac{Z}{d} \right)^{2.25}} \right)}}} \right)^{2}}} & (B)\end{matrix}$

wherein:

Z is expressed in mm

d is expressed in mm

V is expressed in m·s⁻¹

P is expressed in N·m⁻²

In other words, if equation (A) is not observed, equation (B) has to beobserved and vice versa. The equations (A) and (B) may also be observedsimultaneously.

Generally, the parameters V and d are imposed by the production lineused. Therefore, there only remains Z and P or even fO₂, to be adjustedfor meeting the requirements above.

Parameters thus set give the possibility of attaining, aftersolidification of the coating 7 and before a possible skin-pass, awaviness Wa_(0.8) of less than or equal to 0.55 μm as illustrated byExample 1 below.

Still more advantageously, at least one of the following equations isobserved:

$\begin{matrix}{{\frac{Z}{d} + {18{\ln\left( \frac{Z}{d} \right)}}} < {{8{\ln\left( \frac{P}{V} \right)}} - 36.32}} & (C) \\{{fO}_{2} < \frac{2.304{.10}^{- 3}}{\left( {36.32 + \frac{Z}{d} + {8{\ln\left( {\frac{V}{P}\left( \frac{Z}{d} \right)^{2.25}} \right)}}} \right)^{2}}} & (D)\end{matrix}$

wherein:

Z is expressed in mm

d is expressed in mm

V is expressed in m·s⁻¹

P is expressed in N·m⁻²

In other words, if equation (C) is not observed, equation (D) must beobserved and vice versa. The equations (C) and (D) may also be observedsimultaneously.

If the parameters Z, d, V, P and fO₂ satisfy equation (C) and/orequation (D) then, after solidification of the coatings 7 and before apossible skin-pass, a waviness Wa_(0.8) of less than or equal to 0.35 μmis attained.

The coatings 7 are then left to cool in a controlled way so that theysolidify.

As indicated earlier, at the end of this cooling operation 7 the outersurfaces 21 of the coating 7 have wavinesses Wa_(0.8) of less than 0.55μm, or even less than 0.35 μm.

Alternatively, brushing may be carried out in order to remove thecoating 7 deposited on one face 5 so that only one of the faces 5 of thesubstrate 3 will finally be coated with a coating 7.

When the coatings 7 are completely cooled, the metal sheet 1 may undergoa skin-pass operation for giving texture to the outer surfaces 21 of thecoating 7, facilitating subsequent forming process of the metal sheet 1.

Indeed, the skin-pass operation gives the possibility of transferring tothe outer surfaces 21 of the coating 7 of the metal sheet 1 sufficientroughness in order for its forming process to be properly carried out,while promoting good retention of the oil applied on the metal sheet 1before it is formed. The elongation rate of the metal sheet 1 during theskin-pass operation is generally comprised between 0.5 and 2%.

Preferably, the skin-pass operation will give the possibility of keepinga waviness Wa_(0.8) of less than 0.55 μm and preferably less than 0.35μm for the outer surfaces 21 of the coating 7.

In a first alternative, the skin-pass operation will be carried out withEDT work rolls for which the work surfaces have a roughness Ra_(2.5)comprised between 2.05 and 2.95 μm. If the elongation rate during theskin-pass operation is less than or equal to 1.1%, the roughnessRa_(2.5) of the work surfaces of the EDT work rolls will preferably becomprised between 2.50 and 2.95 μm. If the elongation rate during theskin-pass operation is greater than or equal to 1.1%, the roughnessRa_(2.5) of the work surfaces of the EDT work rolls will preferably becomprised between 2.05 and 2.50 μm.

In another alternative, the skin-pass operation will be carried out withEBT work rolls for which the work surfaces have a roughness Ra_(2.5)comprised between 2.90 and 4.10 μm. If the elongation rate during theskin-pass operation is less than or equal to 1.1%, the roughnessRa_(2.5) of the work surfaces of the EBT work rolls will preferably becomprised between 3.50 and 4.10 μm. If the elongation rate during theskin-pass operation is greater than or equal to 1.1%, the roughnessRa_(2.5) of the work surfaces of the EBT work rolls will preferably becomprised between 2.90 and 3.50 μm.

The skin-pass operation is generally carried out for a metal sheet 1intended for manufacturing body parts for automobiles.

When the metal sheet 1 is intended for manufacturing domestic electricappliances, for example this additional operation is not carried out.

The metal sheet 1 having been skin-passed or not may then be cut out andthen undergoes a forming process, for example by drawing, bending orprofiling, in order to form a part which may then be painted in order toform, on each coating 7 a paint film (or a paint system).

In the case of parts for domestic electrical appliances, it is alsopossible to possibly subject the paint films to annealing with physicaland/or chemical means, known per se.

For this purpose, it is possible to have the painted part pass through ahot air or induction oven, or further under UV lamps or under a devicediffusing electron beams.

After deformation, the outer surfaces of the coating 7 of the part havea waviness Wa_(0.8) of less than or equal to 0.60 μm, or even less thanor equal to 0.45 μm, or even less than or equal to 0.43 μm, or even 0.41μm or even further 0.37 μm.

This waviness may for example be measured after 3.5% equi-biaxialdeformation.

Controlling the waviness Wa_(0.8) before a possible skin-pass and aftera possible skin-pass to values of less than or equal to 0.55 μm,respectively 0.35 μm, as described above, allows control of the wavinessWa_(0.8) after deformation to values of less than or equal to 0.60 μm,respectively 0.45 μm, 0.43 μm, 0.41 μm or even 0.37 μm.

For automotive applications, after phosphate-coating, each part isdipped in a cataphoresis bath, and a primer paint layer, a base paintlayer, and optionally a finishing varnish layer are applied insuccession.

Before applying the cataphoresis layer on the part, the latter isdegreased beforehand and then phosphate-coated so as to ensure theadherence of the cataphoresis.

The cataphoresis layer provides the part with additional protectionagainst corrosion. The primer paint layer, generally applied with a gun,prepares the final appearance of the part and protects it against stonechipping and against UVs. The base paint layer gives the part its colorand its final appearance. The varnish layer imparts to the surface ofthe part, good mechanical strength, resistance against aggressivechemical agents and a good surface aspect.

Generally, the weight of the phosphate coating layer is comprisedbetween 1.5 and 5 g/m².

The paint films applied for protecting and guaranteeing an optimumsurface aspect to the parts, for example comprise a cataphoresis layerwith a thickness from 15 to 25 μm, a coat of primer paint with athickness from 35 to 45 μm, and a base coat of paint with a thicknessfrom 40 to 50 μm.

In the cases when the paint films further comprise a varnish layer, thethicknesses of the different paint layers are generally the following:

cataphoresis layer: between 15 and 25 μm, preferably less than 20 μm,

primer paint layer: less than 45 μm,

base paint layer: less than 20 μm, and

varnish layer: less than 55 μm.

The paint films may also not comprise any cataphoresis layer, and onlycomprise a primer paint layer and a base paint layer and optionally avarnish layer.

Preferably, the total thickness of the paint films will be less than 120μm or even 100 μm.

The invention will now be illustrated by tests given as an indicationand not as a limitation.

Example 1—Influence of the Volume Fraction fO₂

The tests conducted in this example aim at showing the positiveinfluence of observing equations (A) and/or (B), or even (C) and/or (D).

The table I below details the conditions of a series of tests conductedwith different values of Z, d, V, P and fO₂ and provides the wavinessesWa_(0.8) measured before a skin-pass, NSKP meaning not having beenskin-passed.

The procedure for measuring the waviness Wa_(0.8) consists of acquiringby mechanical probing (without any shoe) a metal sheet profile with alength of 50 mm, at 45° from the rolling direction. From the signalobtained by probing, the approximation of its general shape with apolynomial of a degree of at least 5 is subtracted. The waviness Wa andthe arithmetic mean roughness Ra is then separated by a Gaussien filterby applying a cut-off of 0.8 mm.

The right columns specify for each test, whether the parameters verifythe equations (A), (B), (C) and (D).

TABLE I Wa_(0.8) Z d V P NSKP Eq Eq Eq Eq Tests (mm) (mm) (m/min) (N/m2)fO₂ (μm) (A) (B) (C) (D) 1 9 1.2 150 38800 0.21 0.36 yes yes no no 2 111.2 150 48200 0.21 0.47 yes yes no no 3 7 1.2 150 26300 1.10⁻⁴ 0.27 yesyes yes yes 4 9 1.2 150 38800 1.10⁻⁴ 0.31 yes yes no yes 5 13 1.2 15059000 1.10⁻⁴ 0.44 no yes no no 6 8 1 120 33100 0.21 0.43 yes yes no no 710 1 120 40700 0.21 0.50 yes yes no no 8 14 1 120 60900 0.21 0.84 no nono no 9 6.5 1 120 32600 1.10⁻⁴ 0.31 yes yes yes yes 10 10 1 120 520001.10⁻⁴ 0.41 yes yes no no 11 14 1 120 64900 1.10⁻⁴ 0.66 no no no no 12 81.5 100 22400 1.10⁻⁴ 0.31 yes yes yes yes 13 15 1.5 100 40800 1.10⁻⁴0.37 yes yes no no

Thus, the use of parameters satisfying equation (A) and/or (B) gives thepossibility of attaining wavinesses before a skin-pass Wa_(0.8) of lessthan 0.55 μm.

The use of parameters satisfying equation (C) and/or (D) gives thepossibility of attaining wavinesses before a skin-pass Wa_(0.8) stillsmaller and less than or equal to 0.35 μm.

Wavinesses before any skin-pass Wa_(0.8) of less than or equal to 0.35μm may in certain cases be reached without observing equations (C)and/or (D), notably by observing equations (A) and/or (B) and by usingsmooth work rolls for the cold-rolling and/or of a particular roughnessfor the skin-pass, as discussed below.

Example 2—Influence of Cold-Rolling with Smooth Work Rolls

The tests conducted in this example aim at showing the positiveinfluence of cold-rolling carried out with smooth work rolls, ascompared with rolling carried out with EDT work rolls, the work surfaceof which have a greater roughness.

For this purpose, steel substrates are subject to cold-rolling in orderto attain a thickness of 0.8 mm, either by using so-called smooth workrolls, the work surfaces of which have a roughness Ra_(2.5) of 0.5 μm,or EDT work rolls for which the work surfaces have a roughness Ra_(2.5)of 3 μm. The substrates 3 are then coated with a zinc coating by hot dipcoating in a zinc bath comprising 0.18% by weight of aluminium, forwhich the temperature is 460° C., and are wiped with nitrogen so as toform a zinc coating having a thickness of 6.5 μm.

After complete cooling of the thereby obtained metal sheet 1, the latterare subject to a skin-pass operation conducted with EBT etched workrolls, the work surfaces of which have a roughness Ra_(2.5) of 5 μm,before being cut out and formed by drawing.

The waviness values Wa_(0.8) of the outer surfaces 21 of the coating 7are measured at the end of each of the steps of the method, i.e. aftercold-rolling (CR), after the skin-pass operation (SKP) and after forming(DEF). The latter is carried out by equi-biaxial deformation of 3.5%with a Marciniak tool.

The results of the measurements of Wa_(0.8) are grouped in table II.

As may be seen, the use of smooth rolling allows reduction in thewaviness Wa_(0.8) regardless whether this is at the end of thecold-rolling, of the skin-pass or of the forming step.

TABLE II Ra_(2.5)(μm) Wa_(0.8) Wa_(0.8) Wa_(0.8) work (μm) (μm) (μm)rolls after after after Eq Eq Eq Eq Tests CR CR SKP DEF (A) (B) (C) (D)14 3 0.52 0.39 0.41 yes yes no no 15 0.5 0.15 0.35 0.34 yes yes no no

Example 3—Influence of the Skin-Pass

The tests carried out in this example aim at ensuring the positiveinfluence of a skin-pass carried out by using work rolls, for which thework surfaces have a certain roughness Ra_(2.5).

For this purpose, steel substrates 3 were subject to cold-rolling inorder to form cold-rolled substrates for which the thickness is 0.7 mm.

The substrates 3 are then coated with a zinc coating by hot dip coatingin a zinc bath comprising 0.18% by weight of aluminium, the temperatureof which is 460° C., and are dried with nitrogen in order to form zinccoatings having a thickness of 6.5 μm.

The thereby obtained metal sheets 1 are divided into two batches.

Before being formed by equi-biaxial deformation of 3.5% with a Marciniaktool, the metal sheets 1 from the first batch are subject to a skin-passcarried out with EDT work rolls and with an elongation rate of 1.4%. Theroughness Ra_(2.5) of the work surfaces is 2.20 μm.

The metal sheets 1 from the second batch are subject to a skin-passoperation with the same elongation rate but with EDT etched work rolls,for which the work surfaces have a roughness Ra_(2.5) of 2.60 μm.

The results of the tests are grouped in table III.

TABLE III Ra_(2.5)(μm) Wa_(0.8) Wa_(0.8) Wa_(0.8) work (μm) (μm) (μm)rolls after after after Eq Eq Eq Eq Tests SKP CR SKP DEF (A) (B) (C) (D)16 2.20 0.42 0.28 0.37 yes yes no no 17 2.60 0.42 0.41 0.47 yes yes nono

What is claimed is:
 1. A steel part comprising: a steel sheet substrate;and a coating on at least one surface of the steel sheet substrate, thecoating comprising between 0.2 and 0.7% by weight of Al, a remainder ofthe metal coating being Zn and inevitable impurities; the steel sheetsubstrate and the coating having at least one deformation; an outersurface of the coating having a waviness Wa_(0.8) of less than or equalto 0.43 μm.
 2. The steel part as recited in claim 1 wherein thedeformation is a biaxial deformation.
 3. The steel part as recited inclaim 2 wherein the deformation is an equi-biaxial deformation.
 4. Thesteel part as recited in claim 3 wherein the deformation is at least3.5% from a flat plane.
 5. The steel part as recited in claim 2 whereinthe deformation is at least 3.5% from a flat plane.
 6. The steel part asrecited in claim 1 wherein the deformation is at least 3.5% from a flatplane.
 7. The steel part as recited in claim 1 wherein the deformationis created by a forming process.
 8. The steel part as recited in claim 7wherein the forming process includes stamping.
 9. The steel part asrecited in claim 7 wherein the forming process includes drawing.
 10. Thesteel part as recited in claim 7 wherein the forming process includesbending.
 11. The steel part as recited in claim 7 wherein the formingprocess includes profiling.
 12. The steel part as recited in claim 1wherein the steel sheet substrate has a thickness between 0.2 and 2 mm.13. The steel part as recited in claim 1 wherein the coating has athickness of less than or equal to 25 μm.
 14. The steel part as recitedin claim 1 wherein the outer surface has a waviness Wa_(0.8) of lessthan or equal to 0.41 μm.
 15. The steel part as recited in claim 1wherein the outer surface has a waviness Wa_(0.8) of less than or equalto 0.37 μm.
 16. The steel part as recited in claim 1 further comprisinga film of paint on the outer surface.
 17. The steel part as recited inclaim 16 wherein a thickness of the film of paint is less than or equalto 120 μm.
 18. The steel part as recited in claim 16 wherein a thicknessof the film of paint is less than or equal to 100 μm.
 19. The steel partas recited in claim 1 wherein coating further includes one or moreadditional elements selected from the following: Si, Sb, Pb, Ti, Ca, Mn,Sn, La, Ce, Cr, Zr or Bi, a weight content of each additional element inthe metal coating being less than 0.3%.
 20. The steel part as recited inclaim 1 wherein the coating consists of Zn, between 0.2 and 0.7% byweight of Al, one or more additional elements selected from thefollowing: Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr or Bi, a weightcontent of each additional element in the metal coating being less than0.3%, and inevitable impurities.
 21. The steel part as recited in claim1 wherein the coating has a weight content of Al of less than or equalto 0.6%.
 22. The steel part as recited in claim 1 wherein the coatinghas a weight content of Al of less than or equal to 0.5%.
 23. A landmotor vehicle part comprising the steel part as recited in claim
 1. 24.A land motor vehicle comprising a body, the body comprising the steelpart as recited in claim
 1. 25. A stamped steel part comprising thesteel part as recited in claim
 1. 26. A method for manufacturing a steelpart comprising: providing a steel sheet substrate; providing a coatingon at least one surface of the steel sheet substrate, the coatingcomprising between 0.2 and 0.7% by weight of Al, a remainder of themetal coating being Zn and inevitable impurities; and deforming thesteel sheet substrate and the coating to create at least onedeformation, an outer surface of the coating after the deforming havinga waviness Wafts of less than or equal to 0.43 μm.
 27. A method formanufacturing a steel part comprising: providing a steel sheet substrateto be deformed into a preselected shape including at least onedeformation; providing a coating on at least one surface of the steelsheet substrate, the coating comprising between 0.2 and 0.7% by weightof Al, a remainder of the metal coating being Zn and inevitableimpurities, and controlling the providing of the coating to have apre-deformation waviness Wa_(0.8) less than or equal to a certain value;and deforming the steel sheet substrate and the coating into thepreselected shape, an outer surface of the coating after the deforminghaving a post-deformation waviness Wa_(0.8) of less than or equal to0.43 μm.